U.S. patent application number 16/982219 was filed with the patent office on 2021-01-28 for suspension control apparatus.
The applicant listed for this patent is HITACHI AUTOMOTIVE SYSTEMS, LTD.. Invention is credited to Ryusuke HIRAO, Nobuyuki ICHIMARU, Kentaro KASUYA.
Application Number | 20210023904 16/982219 |
Document ID | / |
Family ID | 1000005147922 |
Filed Date | 2021-01-28 |
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United States Patent
Application |
20210023904 |
Kind Code |
A1 |
KASUYA; Kentaro ; et
al. |
January 28, 2021 |
SUSPENSION CONTROL APPARATUS
Abstract
A suspension control apparatus includes a control device
configured to control a damping characteristic of each of damping
force adjustable shock absorbers. The control device includes an
external force calculation portion configured to calculate a total
external force working on a vehicle body based on a physical amount
output from a physical amount extraction portion, an operation
force calculation portion configured to calculate an
operation-derived force applied to each of the damping force
adjustable shock absorbers according to a load movement due to an
operation on the vehicle, and a vehicle behavior extraction portion
configured to determine an external force derived from a road
surface input by separating the operation-derived force calculated
by the operation force calculation portion from the total external
force calculated by the external force calculation portion.
Inventors: |
KASUYA; Kentaro;
(Utsunomiya-shi, Tochigi, JP) ; ICHIMARU; Nobuyuki;
(Yokohama-shi, Kanagawa, JP) ; HIRAO; Ryusuke;
(Kamagaya-shi, Chiba, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI AUTOMOTIVE SYSTEMS, LTD. |
Hitachinaka-shi, Ibaraki |
|
JP |
|
|
Family ID: |
1000005147922 |
Appl. No.: |
16/982219 |
Filed: |
September 21, 2018 |
PCT Filed: |
September 21, 2018 |
PCT NO: |
PCT/JP2018/034983 |
371 Date: |
September 18, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60G 17/0165 20130101;
B60G 2400/102 20130101; B60G 17/019 20130101; B60G 2500/104
20130101; B60G 2400/202 20130101; B60G 2204/62 20130101; B60G
2400/82 20130101; B60G 2400/60 20130101; B60G 2400/252 20130101;
B60G 2202/312 20130101 |
International
Class: |
B60G 17/0165 20060101
B60G017/0165; B60G 17/019 20060101 B60G017/019 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2018 |
JP |
2018-060017 |
Claims
1. A suspension control apparatus comprising: damping force
adjustable shock absorbers disposed between a vehicle body and
individual wheels of a vehicle, respectively, the damping force
adjustable shock absorbers each having a damping characteristic
that changes according to an instruction from an outside; a
physical amount extraction portion configured to detect or estimate
a physical amount based on a relative displacement between the
vehicle body and each of the wheels; and a control device
configured to control the damping characteristic of each of the
damping force adjustable shock absorbers, wherein the control
device includes an external force calculation portion configured to
calculate a total external force working on the vehicle body based
on the physical amount output from the physical amount extraction
portion, an operation force calculation portion configured to
calculate an operation-derived force applied to each of the damping
force adjustable shock absorbers according to a load movement due
to an operation on the vehicle, and a vehicle behavior extraction
portion configured to determine an external force derived from a
road surface input by separating the operation-derived force
calculated by the operation force calculation portion from the
total external force calculated by the external force calculation
portion.
2. The suspension control apparatus according to claim 1, wherein
the operation-derived force includes an inertial force generated
due to acceleration/deceleration and steering of the vehicle or a
force generated due to a suspension geometry.
3. The suspension control apparatus according to claim 1, wherein
the physical amount extraction portion includes a vehicle height
sensor.
4. The suspension control apparatus according to claim 1, wherein
the control device includes a vertical force calculation portion
configured to calculate a vertical force on the vehicle body, an
acceleration calculation portion configured to calculate an
acceleration based on the vertical force calculated by the vertical
force calculation portion, a sprung speed estimation portion
configured to estimate a sprung speed of the vehicle body from the
acceleration calculated by the acceleration calculation portion,
and a damping characteristic determination portion configured to
determine the damping characteristic of each of the damping force
adjustable shock absorbers based on the sprung speed estimated by
the sprung speed estimation portion.
5. The suspension control apparatus according to claim 4, further
comprising a mass calculation portion configured to calculate a
mass of the vehicle body based on a displacement calculated by the
physical amount extraction portion, wherein the acceleration
calculation portion calculates the acceleration with use of the
vertical force calculated by the vertical force calculation portion
and the mass calculated by the mass calculation portion.
Description
TECHNICAL FIELD
[0001] The present invention relates to a suspension control
apparatus mounted on a vehicle, such as an automobile, and
configured to control a vibration of the vehicle.
BACKGROUND ART
[0002] Generally, as a suspension control apparatus mounted on a
vehicle, such as an automobile, there is known an apparatus
provided with a damping force adjustable shock absorber capable of
adjusting a damping force between a vehicle body and each axle and
configured to variably control a damping force characteristic
exerted by this shock absorber based on a detection signal from a
vehicle height sensor (for example, refer to PTL 1).
CITATION LIST
Patent Literature
[0003] [PTL 1] Japanese Patent Application Public Disclosure No.
5-38922
SUMMARY OF INVENTION
Technical Problem
[0004] Then, the conventional technique discussed in PTL 1 is
disclosed as a configuration that estimates a sprung state based on
information from the vehicle height sensor and a vehicle CAN
signal. However, a sprung state amount in this case is estimated as
a value containing a mixture of a sprung displacement generated due
to a driver's operation (steering and/or braking) and a relative
displacement generated due to a road surface input. This may lead
to a reduction in the accuracy of estimating the sprung state
amount.
[0005] One of objects of the present invention is to provide a
suspension control apparatus capable of separating the relative
displacement due to the road surface input and the relative
displacement due to the driver's vehicle operation, thereby
allowing it to improve accuracy of estimating a sprung speed, which
is highly contributive to control of ride comfort.
Solution to Problem
[0006] According to one aspect of the present invention, a
suspension control apparatus is provided. This suspension control
apparatus includes damping force adjustable shock absorbers
disposed between a vehicle body and individual wheels of a vehicle,
respectively, and each having a damping characteristic that changes
according to an instruction from an outside, a physical amount
extraction portion configured to detect or estimate a physical
amount based on a relative displacement between the vehicle body
and each of the wheels, and a control device configured to control
the damping characteristic of each of the damping force adjustable
shock absorbers. The control device includes an external force
calculation portion configured to calculate a total external force
working on the vehicle body based on the physical amount output
from the physical amount extraction portion, an operation force
calculation portion configured to calculate an operation-derived
force applied to each of the damping force adjustable shock
absorbers according to a load movement due to an operation on the
vehicle, and a vehicle behavior extraction portion configured to
determine an external force derived from a road surface input by
separating the operation-derived force calculated by the operation
force calculation portion from the total external force calculated
by the external force calculation portion.
[0007] According to the one aspect of the present invention, the
suspension control apparatus can determine the external force
derived from the road surface input by separating the
operation-derived force calculated by the operation force
calculation portion from the total external force calculated by the
external force calculation portion. In other words, the suspension
control apparatus can separate the relative displacement due to the
road surface input and the relative displacement derived from the
driver's operation by subtracting a relative displacement generated
due to an inertial force derived from the driver's operation from
the estimated relative displacement (the physical amount) between
the vehicle body and each of the wheels that is detected by the
physical amount extraction portion such as the vehicle height
sensor. As a result, the suspension control apparatus can improve
the accuracy of estimating the sprung speed, which is highly
contributive to the control of the ride comfort.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a perspective view illustrating an automobile to
which a suspension control apparatus according to a first
embodiment is applied.
[0009] FIG. 2 illustrates a vehicle model used to design a state
estimation portion in the automobile illustrated in FIG. 1.
[0010] FIG. 3 is a control block diagram of a controller that
controls ride comfort on the automobile illustrated in FIG. 1.
[0011] FIG. 4 is a control block diagram specifically illustrating
the state estimation portion illustrated in FIG. 3.
[0012] FIG. 5 illustrates a load movement on the automobile due to
a lateral acceleration.
[0013] FIG. 6 illustrates a load movement on the automobile due to
a longitudinal acceleration.
[0014] FIG. 7 is a schematic view illustrating an operation
principle of a suspension apparatus.
[0015] FIG. 8 is a characteristic line diagram illustrating a
relative displacement at each of four wheels in a timing chart.
[0016] FIG. 9 is a characteristic line diagram illustrating
characteristics of a steering angle, a sprung displacement, a
sprung speed, and an instruction current of the automobile in a
timing chart.
[0017] FIG. 10 is a characteristic line diagram illustrating a
characteristic of a vertical acceleration on the sprung side of the
automobile with respect to a vibration frequency.
[0018] FIG. 11 is a control block diagram specifically illustrating
a state estimation portion according to a second embodiment.
[0019] FIG. 12 is a control block diagram specifically illustrating
a part of a state estimation portion according to a third
embodiment.
[0020] FIG. 13 is a control block diagram specifically illustrating
a part of a state estimation portion according to a fourth
embodiment.
[0021] FIG. 14 is a control block diagram specifically illustrating
a damper response delay calculation portion illustrated in FIG.
13.
[0022] FIG. 15 is a control block diagram illustrating a
characteristic of a damping force determined in consideration of a
response delay according to the fourth embodiment.
[0023] FIG. 16 is a control block diagram illustrating a control
instruction response delay calculation portion according to a fifth
embodiment.
[0024] FIG. 17 is a characteristic line diagram illustrating a
characteristic of a current value determined in consideration of a
delay in a response to the control instruction according to the
fifth embodiment.
DESCRIPTION OF EMBODIMENTS
[0025] In the following description, a suspension control apparatus
according to embodiments of the present invention will be described
in detail with reference to the accompanying drawings based on an
example in which the suspension control apparatus is applied to a
four-wheeled automobile.
[0026] For avoiding the complication of the description, the
suspension control apparatus will be described, adding indexes
indicating front left (FL), front right (FR), rear left (RL), and
rear right (RR) to the reference numerals when focusing on, for
example, the respective positions of wheels of the vehicle. When
front left, front right, rear left, and rear right are collectively
referred to, they will be described with the indexes removed from
the reference numerals. Similarly, the suspension control apparatus
will be described, adding indexes indicating front (F) and rear (R)
to the reference numerals. When front and rear are collectively
referred to, they will be described with the indexes removed from
the reference numerals.
[0027] In FIG. 1, a vehicle body 1 forms a main structure of the
vehicle (the automobile). A front left wheel 2FL, a front right
wheel 2FR, a rear left wheel 2RL, and a rear right wheel 2RR
(hereinafter collectively referred to as wheels 2) are provided
below the vehicle body 1, as illustrated in, for example, FIG. 2.
The wheels 2 include tires 3. The tires 3 function as springs that
absorb, for example, fine roughness of a road surface.
[0028] As illustrated in FIG. 2, a stabilizer 4F is provided
between the front left wheel 2FL and the front right wheel 2FR to,
for example, suppress a roll of the vehicle body 1. A stabilizer 4R
is also similarly provided between the rear left wheel 2RL and the
rear right wheel 2RR. These stabilizers 4 are stabilizer mechanisms
provided on the vehicle. The stabilizers 4 are each mounted on the
vehicle body 1 via, for example, a pair of mounting bushes
laterally spaced apart from each other. The stabilizer 4F on the
front side generates a stabilizer reaction force based on torsional
stiffness due to generation of a roll or a difference in vertical
motion between the front left wheel 2FL and the front right wheel
2FR. Similarly, the stabilizer 4R on the rear side functions to
generate a stabilizer reaction force based on torsional stiffness
due to generation of a roll or a difference in vertical motion
between the rear left wheel 2RL and the rear right wheel 2RR.
[0029] Suspension apparatuses 5 on the front wheel side are
disposed between the vehicle body 1 and the wheels 2 (the front
left wheel 2FL and the front right wheel 2FR). As illustrated in
FIGS. 1 and 2, the suspension apparatuses 5 each include a coil
spring 6 as a suspension spring, and a damping force adjustable
damper (hereinafter referred to as a damper 7) as a damping force
adjustable shock absorber disposed between the vehicle body 1 and
each of the two wheels (the front left wheel 2FL and the front
right wheel 2FR) in parallel with this coil spring 6. Suspension
apparatuses 8 on the rear wheel side are disposed between the
vehicle body 1 and the wheels 2 (the rear left wheel 2RL and the
rear right wheel 2RR). The suspension apparatuses 8 each include a
coil spring 9 as a suspension spring, and the damper 7 disposed
between the vehicle body 1 and each of the wheels 2 (the rear left
wheel 2RL and the rear right wheel 2RR) in parallel with this coil
spring 9.
[0030] The suspension apparatuses 5 and 8 on the front and rear
wheel sides may be configured to use, for example, air springs (not
illustrated) of air suspensions instead of the coil springs 6 and 9
as the suspension springs. In this case, a vehicle height, which is
the distance between the wheel 2 and the vehicle body 1, can be
adjusted by supplying or discharging hydraulic fluid (compressed
air) to or from each of the air springs on the front left wheel
2FL, front right wheel 2FR, rear left wheel 2RL, and rear right
wheel 2RR sides.
[0031] Now, the damper 7 of each of the suspension apparatuses 5
and 8 on the front and rear wheel sides is constructed with use of
a damping force adjustable hydraulic shock absorber, such as a
semi-active damper. This damper 7 is equipped with an actuator 7A
embodied by a damping force adjustment valve or the like for
adjusting the characteristic of the generated damping force (a
damping force characteristic) from a hard characteristic (a high
characteristic) to a soft characteristic (a low characteristic).
The actuator 7A is driven by an instruction from the outside and
the flow of the hydraulic fluid is variably controlled, by which
the damping characteristic of each of the dampers 7 is changed.
More specifically, the damping force characteristic (i.e., the
damping characteristic) of the damper 7 is adjusted according to a
relative speed between the vehicle body 1 and the wheel 2 and a
target damping coefficient (a corrected damping coefficient). In
other words, a controller 11 outputs an instruction current i
(refer to FIG. 3) according to the relative speed and the target
damping coefficient. The damper 7 generates a damping force
according to the instruction current i output from the controller
11.
[0032] Four vehicle height sensors 10 in total are provided on the
individual wheel (the front left wheel 2FL, the front right wheel
2FR, the rear left wheel 2RL, and the rear right wheel 2RR) sides
of the vehicle body 1. These vehicle height sensors 10 are vehicle
height detection devices, and individually detect vehicle heights
according to extension or compression of the suspension apparatuses
5 and 8 as the respective vehicle heights on the wheel 2 sides. The
four vehicle height sensors 10 in total output detection signals
indicating the respective vehicle heights to the controller 11.
These vehicle height sensors 10 form a physical amount extraction
portion that detects or estimates a physical amount based on a
relative displacement between the vehicle body 1 and each of the
wheels 2 (i.e., a vertical force and/or a vertical position).
However, for example, an acceleration sensor that generally
acquires the relative displacement is not included in the physical
amount extraction portion. As a specific example of the physical
amount extraction portion, for example, a load sensor on each of
the wheel sides may be employed besides the vehicle height sensor.
Besides them, a system configuration using a laser sensor can also
be employed as long as this system can calculate the relative
displacement.
[0033] The controller 11 includes a microcomputer and the like, and
forms a control device that controls the damping characteristic of
the damper 7. An input side of the controller 11 is connected to
the vehicle height sensors 10, and is also connected to a CAN 12 (a
Controller Area Network) to which various kinds of vehicle
information represented by an acceleration/deceleration, a vehicle
speed, and a steering angle of the vehicle are transmitted. The
controller 11 can acquire the information such as the
acceleration/deceleration, the vehicle speed, and the steering
angle of the vehicle via the CAN 12. Further, an output side of the
controller 11 is connected to each of the actuators 7A of the
dampers 7. The controller 11 estimates a sprung speed of the
vehicle body 1 based on the information such as the above-described
vehicle height, acceleration/deceleration, vehicle speed, and
steering angle. The controller 11 calculates the damping
characteristic that the damper 7 should generate based on the
estimated sprung speed. The controller 11 outputs the instruction
current i according to the damping characteristic determined as a
result of the calculation to the actuator 7A, thereby controlling
the damping characteristic of the damper 7.
[0034] As illustrated in FIG. 3, the controller 11 includes a state
estimation portion 13 and a calculation portion 14. The state
estimation portion 13 estimates the state of the vehicle. The
calculation portion 14 determines the damping characteristic (i.e.,
the instruction current i) based on a result of the estimation by
the state estimation portion 13. This calculation portion 14
estimates the above-described sprung speed based on a road surface
disturbance relative speed, which will be described below, as a
result of the estimation by the state estimation portion 13, and
determines the damping force characteristic that the damper 7
should generate based on the estimated sprung speed. Further, the
calculation portion 14 of the controller 11 outputs the instruction
current i according to the above-described damping characteristic
to the actuator 7A, thereby variably controlling the damping
characteristic of the damper 7.
[0035] As illustrated in FIG. 4, the state estimation portion 13 of
the controller 11 includes an external force calculation portion
15, a signal processing portion 16, a vertical force calculation
portion 17, a damper damping force estimation portion 18, a
front-wheel spring force estimation portion 19, and a vertical
relative acceleration calculation portion 20, and further includes
a relative speed calculation portion 21, a relative displacement
calculation portion 22, and a vehicle behavior extraction portion
23. The external force calculation portion 15 serves as an external
force calculation portion that calculates a total external force
(including, for example, a road surface input and an input derived
from a driver) working on the vehicle body 1 based on the vehicle
height sensor value output from each of the vehicle height sensors
10 (i.e., the physical amount acquired by the physical amount
extraction portion) and the CAN information. The signal processing
portion 16 processes a signal from the CAN 12. The vertical force
calculation portion 17 serves as a vertical force calculation
portion that calculates the vertical force on the vehicle body 1.
The vertical relative acceleration calculation portion 20
calculates a vertical relative acceleration derived from the
driver's input based on a net force (total force) of forces
generated on the sprung side due to the driver's input. The vehicle
behavior extraction portion 23 serves as a road surface disturbance
relative displacement calculation portion. In a case where the
vehicle height sensor value is used as the physical amount of the
physical amount extraction portion, a total vehicle height value
including an amount corresponding to a vehicle height change due to
the total external force is acquired as the value output from the
external force calculation portion 15.
[0036] The above-described signal processing portion 16 includes an
FB control instruction portion 16A, a lateral acceleration
calculation portion 16B, a sprung mass calculation portion 16C, and
a longitudinal acceleration calculation portion 16D. The FB control
instruction portion 16A outputs an FB (feedback) control
instruction based on a signal from an actual instruction value
measured by the CAN 12 or the controller 11. The lateral
acceleration calculation portion 16B calculates a lateral
acceleration Ay working on the vehicle based on a signal from the
CAN 12 (for example, the steering angle signal and the vehicle
speed signal of the vehicle).
[0037] Then, the longitudinal acceleration calculation portion 16D
functions to calculate a longitudinal acceleration Ax working on
the vehicle based on a signal from the CAN 12 (for example, the
acceleration signal and/or the deceleration signal of the vehicle).
The above-described sprung mass calculation portion 16C functions
to estimate the mass (a sprung mass M) of the vehicle body 1
according to a signal from the CAN 12. In this case, the sprung
mass calculation portion 16C may be configured to use a
predetermined value as the mass (the sprung mass M) of the vehicle
body 1. The sprung mass calculation portion 16C may calculate the
mass of the vehicle body 1 with use of the value of the vehicle
height sensor (the vehicle height value).
[0038] The vertical force calculation portion 17 of the state
estimation portion 13 includes, for example, a front-wheel jack-up
force estimation portion 17A, a portion 17B for calculating a load
change due to the lateral acceleration Ay, a front-wheel
anti-dive/squat force estimation portion 17C, and a portion 17D for
calculating a load change due to the longitudinal acceleration Ax.
The vertical force calculation portion 17 forms the external force
calculation portion together with the damper damping force
estimation portion 18 and the front-wheel spring force estimation
portion 19. This external force calculation portion functions to
calculate an operation-derived force applied to the damper 7 (the
damping force adjustable shock absorber) at each of the wheels
according to a load movement due to an operation on the vehicle
(including a driving operation by the driver and an autonomous
driving operation without the intervention of the driver).
[0039] The front-wheel jack-up force estimation portion 17A
determines jack-up/down forces JFFL, JFFR, JFRL, and JFRR by
estimating and calculating them with use of equations 10 to 17,
which will be described below, based on the lateral acceleration Ay
calculated by the lateral acceleration calculation portion 16B. The
portion 17B for calculating the load change due to the lateral
acceleration Ay calculates a change in a load .DELTA.W applied to
each of the wheels 2 (i.e., wheel loads .DELTA.WFL, .DELTA.WFR,
.DELTA.WRL, and .DELTA.WRR) with use of equations 3 to 7, which
will be described below, based on the sprung mass M calculated by
the sprung mass calculation portion 16C and the above-described
lateral acceleration Ay.
[0040] The front-wheel anti-dive/squat force estimation portion 17C
determines front-wheel anti-dive/squat forces GFFL, GFFR, GFRL, and
GFRR with use of equations 22 to 29, which will be described below,
based on the longitudinal acceleration Ax calculated by the
longitudinal acceleration calculation portion 16D. The portion 17D
for calculating the load change due to the longitudinal
acceleration Ax calculates a change in a load .DELTA.WAx generated
at each of the wheels due to the longitudinal acceleration Ax with
use of equations 18 and 19, which will be described below, based on
the sprung mass M calculated by the sprung mass calculation portion
16C and the above-described longitudinal acceleration Ax.
[0041] The damper damping force estimation portion 18 of the state
estimation portion 13 forms a damping characteristic determination
portion that determines the damping characteristic of the damper 7
at each of the wheels based on an instruction from the FB control
instruction portion 16A and a relative speed (.DELTA.X21offset/dt)
as an estimated sprung speed calculated by the relative speed
calculation portion 21 (a sprung speed estimation portion), which
will be described below. In other words, the damper damping force
estimation portion 18 determines a damper damping force Fda by
estimating and calculating it as indicated by the following
equation 2. In this equation, a coefficient c is a damping
coefficient.
.DELTA.X.sub.21.sub.offset/dt=.DELTA.{dot over
(X)}.sub.21.sub.offset [Equation 1]
F.sub.da=c.DELTA.{dot over (X)}.sub.21.sub.offset [Equation 2]
[0042] The front-wheel spring force estimation portion 19 has a
function of estimating and calculating a spring force Fsp working
on the front wheel (the front left wheel 2FL and the front right
wheel 2ER) based on a relative displacement (.DELTA.X21offset)
calculated by the relative displacement calculation portion 22,
which will be described below, as a front-wheel spring force
(Fsp=k.DELTA.X21offset). The coefficient k is a spring constant. A
delay operator 24 is provided between the damper damping force
estimation portion 18 and the relative speed calculation portion
21. Further, another delay operator 25 is provided between the
front-wheel spring force estimation portion 19 and the relative
displacement calculation portion 22.
[0043] The vertical relative acceleration calculation portion 20
calculates a relative acceleration .alpha. by summing up the
vertical force calculated by the vertical force calculation portion
17 (i.e., the jack-up/down force JFFL, JFFR, JFRL, or JFRR
estimated by the front-wheel jack-up force estimation portion 17A,
the change in the load .DELTA.W applied to each of the wheels 2
that is calculated by the load change calculation portion 17B, the
front-wheel anti-dive/squat force GFFL, GFFR, GFRL, or GFRR
estimated by the front-wheel anti-dive/squat force estimation
portion 17C, and the change in the load .DELTA.WAx calculated by
the load change calculation portion 17D), the damper damping force
Fda according to the above-described equation 2 that is estimated
by the damper damping force estimation portion 18, and the
front-wheel spring force (Fsp=k.DELTA.X21offset) estimated by the
front-wheel spring force estimation portion 19 as indicated by an
equation 34, which will be described below, to thus calculate a net
force Ma of the operation-derived forces while adding up the
respective forces (.DELTA.W, .DELTA.WAx, JF, and GF), and dividing
this net force Ma by the mass M.
M.sub..alpha.=M.DELTA.{umlaut over (X)}.sub.21.sub.offset [Equation
3]
.alpha.=.DELTA.{umlaut over (X)}.sub.21.sub.offset [Equation 4]
[0044] The relative speed calculation portion 21 illustrated in
FIG. 4 calculates the relative speed (.DELTA.X21offset/dt) by
integrating the relative acceleration a calculated by the relative
acceleration calculation portion 20. The relative displacement
calculation portion 22 calculates the relative displacement
(.DELTA.X21offset) by integrating the relative speed
(.DELTA.X21offset/dt) calculated by the relative speed calculation
portion 21.
[0045] The vehicle behavior extraction portion 23 forms a vehicle
behavior extraction portion that determines the external force
derived from the road surface input by separating the
above-described operation-derived force calculated by the
above-described operation force calculation portion from the
above-described total external force calculated by the external
force calculation portion 15. In other words, the vehicle behavior
extraction portion 23 functions to calculate a relative
displacement due to a road surface disturbance (i.e., the road
surface disturbance relative displacement) by subtracting the
relative displacement (.DELTA.X21offset) due to the driver's
operation from the sensor value acquired by the vehicle height
sensor 10.
[0046] In other words, the state estimation portion 13 of the
controller 11 (the control device) includes the vertical force
calculation portion 17, the relative acceleration calculation
portion 20, the relative speed calculation portion 21, and the
damper damping force estimation portion 18 (the damping
characteristic determination portion). The vertical force
calculation portion 17 serves as the vertical force calculation
portion that calculates the vertical force on the vehicle body 1.
The relative acceleration calculation portion 20 serves as an
acceleration calculation portion that calculates the acceleration a
based on the vertical force calculated by the vertical force
calculation portion 17. The relative speed calculation portion 21
serves as a sprung speed estimation portion that estimates the
relative speed (.DELTA.X21offset/dt) as the sprung speed of the
vehicle body 1 based on the acceleration a calculated by the
relative acceleration calculation portion 20. The damper damping
force estimation portion 18 estimates the damping characteristic of
the damper 7 at each of the wheels based on the relative speed
(.DELTA.X21offset/dt) calculated by the relative speed calculation
portion 21 as the damper damping force Fda according to the
above-described equation 2.
[0047] Among them, the vertical force calculation portion (for
example, the front-wheel jack-up force estimation portion 17A, the
portion 17B for calculating the load change due to the lateral
acceleration Ay, the front-wheel anti-dive/squat force estimation
portion 17C, and the portion 17D for calculating the load change
due to the longitudinal acceleration Ax) forms the external force
calculation portion that calculates the operation-derived force
applied to the damper 7 (the damping force adjustable shock
absorber) at each of the wheels according to the load movement due
to the operation on the vehicle (including the driving operation by
the driver and the autonomous driving operation force without the
intervention of the driver) together with the damper damping force
estimation portion 18 and the front-wheel spring force estimation
portion 19.
[0048] For example, the relative displacement generated due to the
driver's operation while the vehicle is running is calculated based
on the load movement and the jack-up/down force generated due to
the lateral acceleration Ay as illustrated in FIG. 5 and the load
movement and the lift-up/down force generated due to the
longitudinal acceleration Ax as illustrated in FIG. 6. FIGS. 5 and
6 illustrate how the vehicle behaves under a situation that these
forces are applied.
[0049] As illustrated in FIG. 5, relative displacements X21left and
X21right for controlling the ride comfort are calculated by adding
and subtracting .DELTA.X21offset to and from the detection value (a
relative displacement X21) of the vehicle height sensor 10 as
indicated by the following equations 5 and 6, assuming that
.DELTA.X21'offset represents the relative displacement generated
due to the lateral acceleration Ay between the vehicle body 1 and
the wheel 2.
X.sub.21.sub.left=X.sub.21+.DELTA.X'.sub.21.sub.offset [Equation
5]
X.sub.21.sub.right=X.sub.21+.DELTA.X'.sub.21.sub.offset [Equation
6]
[0050] Next, the load .DELTA.W applied to each of the wheels 2
(i.e., the wheel loads .DELTA.WFL, .DELTA.WFR, .DELTA.WRL, and
.DELTA.WRR) can be calculated from the following equations 7 to 10,
assuming that hg [m] represents the height of a sprung center of
gravity G, Ay [m/s.sup.2] represents the lateral acceleration,
.theta.roll [degrees] represents a roll angle generated due to the
roll, M [kg] represents the sprung mass as the vehicle weight, and
T [m] represents a vehicle width. A half width T/2 of the vehicle
width T illustrated in FIG. 2 is a dimension corresponding to
widths TFl, TFr, TRl, and TRr in the equations 7 to 10. In this
case, the load .DELTA.W may be calculated assuming that the roll
angle .theta.roll is zero (.theta.roll=0) as indicated by the
following equation 11 for the simplification of the
calculation.
.DELTA. W FL = - Ay 2 hg cos .theta. roll M Fl T Fl [ Equation 7 ]
.DELTA. W FR = Ay 2 hg cos .theta. roll M Fr T Fr [ Equation 8 ]
.DELTA. W R L = - Ay 2 hg cos .theta. roll M Rl T Rl [ Equation 9 ]
.DELTA. W R R = Ay 2 hg cos .theta. roll M Rr T Rr [ Equation 10 ]
cos .theta. roll .apprxeq. 1 [ Equation 11 ] ##EQU00001##
[0051] The change in the load .DELTA.W at each of the wheels (i.e.,
the wheel loads .DELTA.WFL, .DELTA.WFR, .DELTA.WRL, and .DELTA.WRR)
generated due to the lateral acceleration Ay calculated from the
above-described equations 7 to 10 becomes equal to a value
calculated by multiplying the relative acceleration ay by the
sprung mass M at each of the wheels as indicated by the following
equations 12 and 13, and therefore the relative acceleration ay can
be calculated based on the load .DELTA.W generated at each of the
wheels and the relative displacement (.DELTA.X21offset) is
calculated by integrating this value.
.alpha..gamma.=.DELTA.{umlaut over (X)}.sub.21.sub.offset [Equation
12]
.DELTA.W=M.DELTA.{umlaut over (X)}.sub.21.sub.offset [Equation
13]
[0052] Further, the jack-up/down forces JFFL, JFFR, JFRL, and JFRR
can be expressed by the following equations 14 to 17 when the
lateral acceleration Ay is positive (Ay>0). In these equations,
coefficients PCFl, NCFr, PCRl, and NCRr are proportional
coefficients.
JF.sub.Fl=PC.sub.Fl.times.Ay [Equation 14]
JF.sub.FR=-NC.sub.FR.times.Ay [Equation 15]
JF.sub.RL=PC.sub.Rl.times.Ay [Equation 16]
JF.sub.RR=-NC.sub.Rr.times.Ay [Equation 17]
[0053] When the lateral acceleration Ay is equal to or smaller than
zero (Ay.ltoreq.0), the jack-up/down forces JFFL, JFFR, JFRL, and
JFRR are calculated from the following equations 18 to 21. In these
equations, coefficients NCFl, PCFr, NCRl, and PCRr are proportional
coefficients.
JF.sub.Fl=NC.sub.Fl.times.Ay [Equation 18]
JF.sub.FR=-PC.sub.Fr.times.Ay [Equation 19]
JF.sub.RL=NC.sub.Rl.times.Ay [Equation 20]
JF.sub.RR=-PC.sub.Rr.times.Ay [Equation 21]
[0054] On the other hand, the change in the load .DELTA.WAx
generated at each of the wheels due to the longitudinal
acceleration Ax can be calculated from the following equation 22,
assuming that .DELTA.X21offset represents the relative displacement
generated due to the longitudinal acceleration Ax, hg represents
the height of the sprung center of gravity G, Lwbs represents the
dimension of the wheelbase, Ax [m/s.sup.2] represents the
longitudinal acceleration, .theta.pitch [degrees] represents a
pitch angle generated due to a pitch, and M [kg] represents the
sprung mass as the vehicle weight as illustrated in FIG. 6. Assume
that the generated pitch angle .theta.pitch is a value
approximately equal to zero (.theta.pitch.apprxeq.0) as indicated
by the following equation 23 for the simplification of the
calculation.
.DELTA. WAx = 2 Axhg ( M Fr + M Rr ) cos .theta. pitch 2 Lwbs [
Equation 22 ] cos .theta. pitch .apprxeq. 1 [ Equation 23 ]
##EQU00002##
[0055] The relative acceleration ax generated due to the
longitudinal acceleration Ax can be expressed as the following
equation 24, and the change in the load .DELTA.WAx generated at
each of the wheels due to the longitudinal acceleration Ax can be
expressed as the following equation 25.
.alpha..times.=.DELTA.{umlaut over (X)}.sub.21 .sub.offset
[Equation 24]
.DELTA.WAx=M.DELTA.{umlaut over (X)}.sub.21 .sub.offset [Equation
25]
[0056] The lift-up/down force (i.e., the front-wheel
anti-dive/squat forces GFFL, GFFR, GFRL, and GFRR) due to the
suspension geometry is generated on the sprung portion of the
vehicle body 1 side according to the dive/squat generated due to
the longitudinal acceleration Ax. These forces GFFL, GFFR, GFRL,
and GFRR are in a proportional relationship with the longitudinal
acceleration Ax. Therefore, when the longitudinal acceleration Ax
is positive (Ax>0), the front-wheel anti-dive/squat forces GFFL,
GFFR, GFRL, and GFRR can be calculated from the following equations
26 to 29. In these equations, coefficients ACFl, ACFr, ACRl, and
ACRr are proportional coefficients when the vehicle is
accelerated.
GF.sub.FL=-AC.sub.Fl.times.Ax [Equation 26]
GF.sub.FR=-AC.sub.Fr.times.Ax [Equation 27]
GF.sub.RL=AC.sub.Rl.times.Ax [Equation 28]
GF.sub.RR=AC.sub.Rr.times.Ax [Equation 29]
[0057] When the longitudinal acceleration Ax is equal to or smaller
than zero (Ax.ltoreq.0), the front-wheel anti-dive/squat forces
GFFL, GFFR, GFRL, and GFRR can be calculated from the following
equations 30 to 33. In these equations, coefficients DCFl, DCFr,
DCRl, and DCRr are proportional coefficients when the vehicle is
decelerated.
GF.sub.FL=DC.sub.Fl.times.Ax [Equation 30]
GF.sub.FR=DC.sub.Fr.times.Ax [Equation 31]
GF.sub.RL=-DC.sub.Rl.times.Ax [Equation 32]
GF.sub.RR=-DC.sub.Rr.times.Ax [Equation 33]
[0058] The vertical relative acceleration calculation portion 20
illustrated in FIG. 4 calculates the net force Ma derived from the
operation by summing up the jack-up/down force JFFL, JFFR, JFRL, or
JFRR estimated by the front-wheel jack-up force estimation portion
17A from the above-described equations 14 to 21, the change in the
load .DELTA.W applied to each of the wheels 2 that is calculated by
the load change calculation portion 17B from the above-described
equations 7 to 13, the front-wheel anti-dive/squat force GFFL,
GFFR, GFRL, or GFRR estimated by the front-wheel anti-dive/squat
force estimation portion 17C from the above-described equations 26
to 33, the change in the load .DELTA.WAx calculated by the load
change calculation portion 17D, the damper damping force Fda
estimated by the damper damping force estimation portion 18 from
the above-described equations 26 to 33, and the front-wheel spring
force (k.DELTA.X21offset) estimated by the front-wheel spring force
estimation portion 19 as indicated by the equation 34, which will
be described below, to add up the respective forces (.DELTA.W,
.DELTA.WAx, JF, and GF). After that, the vertical relative
acceleration calculation portion 20 calculates the relative
acceleration a as indicated by the above-described equations 3 and
4 by dividing the net force Ma by the mass M.
.DELTA.W+.DELTA.WAx+JF+GF-k.DELTA.X.sub.21.sub.offset-c.DELTA.{dot
over (X)}.sub.21.sub.offset=M.DELTA.{umlaut over
(X)}.sub.21.sub.offset [Equation 34]
[0059] The suspension control apparatus according to the first
embodiment is configured in the above-described manner, and a
control operation thereof will be described next.
[0060] The state estimation portion 13 of the controller 11
estimates the sprung state amount based on the vehicle height
information from each of the vehicle height sensors 10 and the
signal from the CAN 12. However, the sprung state amount in this
case may be estimated with reduced accuracy unless the sprung
displacement generated due to the driver's operation (the steering
and/or the braking) and the relative displacement generated due to
the road surface input are separated from each other as indicated
in, for example, an operational principle diagram of the suspension
apparatuses 5 and 8 illustrated in FIG. 7.
[0061] Therefore, in the first embodiment, the vertical relative
acceleration calculation portion 20 of the state estimation portion
13 calculates the net force Ma of the operation-derived forces by
summing up the jack-up/down force JFFL, JFFR, JFRL, or JFRR
estimated by the front-wheel jack-up force estimation portion 17A,
the change in the load .DELTA.W applied to each of the wheels 2
that is calculated by the load change calculation portion 17B, the
front-wheel anti-dive/squat force GFFL, GFFR, GFRL, or GFRR
estimated by the front-wheel anti-dive squat force estimation
portion 17C, the change in the load .DELTA.WAx calculated by the
load change calculation portion 17D, the damper damping force Fda
estimated by the damper damping force estimation portion 18 from
the above-described equation 2, and the front-wheel spring force
(Fsp=k.DELTA.X21offset) estimated by the front-wheel spring force
estimation portion 19 as indicated by the above-described equation
34. Then, the vertical relative acceleration calculation portion 20
calculates the relative acceleration a by dividing this net force
Ma by the mass M.
[0062] Next, the relative speed calculation portion 21 estimates
and calculates the relative speed (.DELTA.X21offset/dt) as the
sprung speed of the vehicle body 1 based on the relative
acceleration .alpha. calculated by the relative acceleration
calculation portion 20, and the relative displacement calculation
portion 22 calculates the relative speed (.DELTA.X21offset) by
integrating the above-described relative speed
(.DELTA.X21offset/dt). In other words, the relative displacement
calculation portion 22 calculates the relative displacement
(.DELTA.X21offset) generated from the inertial force derived from
the driver's operation and the force generated due to the
suspension geometry such as the jack-up/down force and the
lift-up/down force as a vehicle inertial influence relative
displacement.
[0063] After that, the vehicle behavior extraction portion 23
determines the external force derived from the road surface input
by separating the above-described operation-derived force
calculated by the above-described operation force calculation
portion from the total external force calculated by the external
force calculation portion 15. In other words, the vehicle behavior
extraction portion 23 calculates the relative displacement due to
the road surface disturbance (i.e., the road surface disturbance
relative displacement) by subtracting the relative displacement
(.DELTA.X21offset) due to the driver's operation from the sensor
value acquired by the vehicle height sensor 10.
[0064] In this manner, according to the first embodiment, the
suspension control apparatus can calculate the relative
displacement due to the road surface disturbance alone as the road
surface disturbance relative displacement by separating the
relative displacement due to the road surface input (the sensor
value acquired by the vehicle height sensor 10) and the relative
displacement derived from the driver's operation
(.DELTA.X21offset). As a result, the suspension control apparatus
can improve the accuracy of estimating the sprung speed, which is
highly contributive to the control of the ride comfort, thereby
effectively controlling the ride comfort in correspondence with the
road surface input.
[0065] More specifically, the relative displacement signal
generated due to the road surface input (i.e., the road surface
disturbance relative displacement) can be input to the calculation
portion 14 illustrated in FIG. 3 by removing the relative
displacement generated from the inertial force generated due to the
driver's operation such as acceleration/deceleration and steering
when the vehicle is running and the force generated due to the
suspension geometry such as the jack-up/down force and the
lift-up/down force from the sensor value measured by each of the
vehicle height sensors 10.
[0066] After that, the calculation portion 14 estimates the
above-described sprung speed based on the road surface disturbance
relative displacement as a result of the estimation by the state
estimation portion 13, determines the damping characteristic that
the damper 7 should generate based on the estimated sprung speed,
and outputs the instruction current i according to this damping
characteristic to the actuator 7A, thereby being able to variably
control the damping characteristic of the damper 7.
[0067] Then, a running test was conducted by mounting the
suspension control apparatus according to the present embodiment on
an actual vehicle and driving this vehicle on a wavy road to verify
the effectiveness of the vehicle state estimation according to the
present embodiment. FIGS. 8 to 10 each illustrate the
characteristic of the result of this test. In this case, the
vehicle was driven in a running pattern of repeatedly entering and
exiting the wavy road while turning, and a combined influence of
the road surface input due to the wavy road and the behavior on the
sprung side due to the steering was able to be evaluated.
[0068] A characteristic line 31 indicated by a solid line in FIG. 8
represents the characteristic of the relative displacement signal
generated due to the road surface input (i.e., the road surface
disturbance relative displacement) on the front right wheel 2FR
side. On the other hand, a characteristic line 32 indicated by a
dotted line represents the characteristic of the sensor value
measured by the vehicle height sensor 10 on the front right wheel
2FR side. A characteristic line 33 indicated by a solid line in
FIG. 8 represents the characteristic of the relative displacement
signal generated due to the road surface input (i.e., the road
surface disturbance relative displacement) on the front left wheel
2FL side. On the other hand, a characteristic line 34 indicated by
a dotted line represents the characteristic of the sensor value
measured by the vehicle height sensor 10 on the front left wheel
2FL side.
[0069] A characteristic line 35 indicated by a solid line in FIG. 8
represents the characteristic of the relative displacement signal
generated due to the road surface input (i.e., the road surface
disturbance relative displacement) on the rear right wheel 2RR
side. On the other hand, a characteristic line 36 indicated by a
dotted line represents the characteristic of the sensor value
measured by the vehicle height sensor 10 on the rear right wheel
2RR side. Next, a characteristic line 37 indicated by a solid line
in FIG. 8 represents the characteristic of the relative
displacement signal generated due to the road surface input (i.e.,
the road surface disturbance relative displacement) on the rear
left wheel 2RL side. On the other hand, a characteristic line 34
indicated by a dotted line represents the characteristic of the
sensor value measured by the vehicle height sensor 10 on the rear
left wheel 2RL side.
[0070] The characteristic lines 31, 33, 35, and 37 (the road
surface disturbance relative displacement) according to the present
embodiment indicated by the solid lines in FIG. 8 are confirmed to
be characteristics of relatively smooth displacements compared to
the characteristic lines 32, 34, 36, and 38 (the sensor values of
the vehicle height sensors 10) indicated by the dotted lines, and
allow the present embodiment to be evaluated to improve the ride
comfort performance.
[0071] A characteristic line 39 indicated by a solid line in FIG. 9
represents the characteristic of the steering angle according to
the present embodiment when the vehicle ran while turning on the
wavy road. A characteristic line 40 indicated by a dotted line in
FIG. 9 represents the change in the steering angle according to the
conventional technique (i.e., when the relative displacement
derived from the driver's operation and the relative displacement
derived from the road surface input were not separated). Further, a
characteristic line 41 indicated by a solid line represents the
characteristic of the sprung displacement according to the present
embodiment (i.e., when the relative displacement derived from the
driver's operation and the relative displacement derived from the
road surface input were separated). On the other hand, a
characteristic line 42 indicated by a dotted line represents the
characteristic of the sprung displacement according to the
conventional technique.
[0072] A characteristic line 43 indicated by a solid line in FIG. 9
represents the characteristic of the sprung speed according to the
present embodiment when the vehicle ran while turning on the wavy
road. On the other hand, a characteristic line 44 indicated by a
dotted line represents the characteristic of the sprung speed
according to the conventional technique. Further, a characteristic
line 45 indicated by a solid line represents the characteristic of
the instruction current according to the present embodiment (i.e.,
when the relative displacement derived from the driver's operation
and the relative displacement derived from the road surface input
were separated). A characteristic line 46 indicated by a dotted
line represents the characteristic of the instruction current
according to the conventional technique.
[0073] The characteristic lines 40 to 46 illustrated in FIG. 9 make
it clear that the instruction current was output as an incorrect
instruction as understood from the characteristic line 46 according
to the conventional technique indicated by the dotted line at a
timing when the steering input and the input of the wavy road were
fed in combination (for example, time t1 to time t2 in FIG. 9). For
this reason, it is considered that the conventional technique led
to the deterioration of the ride comfort as a whole due to this
incorrect instruction. More specifically, it is considered that the
conventional technique misinterpreted the sprung displacement
generated due to the driver's input as the displacement derived
from the road surface input, and performed erroneous control.
[0074] A characteristic line 47 indicated by a solid line in FIG.
10 represents a PSD value of the sprung acceleration according to
the present embodiment as a relationship with a vibration
frequency. A characteristic line 48 indicated by a dotted line in
FIG. 10 represents a PSD value of the sprung acceleration according
to the conventional technique (i.e., when the relative displacement
derived from the driver's operation and the relative displacement
derived from the road surface input were not separated). The
characteristic line 47 (the PSD value of the sprung acceleration
according to the present embodiment) also makes it clear that the
ride comfort on the vehicle was improved as a whole compared to the
conventional technique (the characteristic line 48).
[0075] In this manner, according to the first embodiment, the
suspension control apparatus can improve the accuracy of the sprung
estimation to thus improve the ride comfort performance by
performing control of separating the relative displacement derived
from the driver's operation and the relative displacement derived
from the road surface input. In other words, because of the
reduction in incorrect instructions like the example issued by the
conventional technique, the suspension control apparatus can
improve the ride comfort in a high-frequency region as understood
from the characteristic line 47 indicated by the solid line in FIG.
10.
[0076] Therefore, according to the first embodiment, the suspension
control apparatus becomes able to improve the accuracy of
estimating the sprung speed for controlling the ride comfort due to
the influence of the driver's acceleration/deceleration and
steering on the sprung behavior, thereby becoming able to improve
the ride comfort performance on the vehicle (the automobile)
illustrated in, for example, FIGS. 1 and 2. Further, the suspension
control apparatus can improve the accuracy of the estimated value
of the relative displacement generated according to the type and
specifications of the suspension by taking into consideration the
jack-up/down force and the lift-up/down force generated due to the
driver's operation that are derived from the suspension
geometry.
[0077] Further, according to the first embodiment, the suspension
control apparatus can reduce the incorrect control of the ride
comfort control when the vehicle turns or is
accelerated/decelerated to thus improve the ride comfort
performance, by separating the relative displacement due to the
driver's operation and the relative displacement due to the road
surface input. In addition, the suspension control apparatus can
realize a ride comfort performance equivalent to the conventional
system using a sprung acceleration sensor despite using only the
vehicle height sensor 10, thereby increasing the market value of
the semi-active suspension system using the vehicle height sensor
10.
[0078] Next, FIG. 11 illustrates a second embodiment. The present
embodiment is characterized by estimating the sprung mass based on
the displacement calculated by the physical amount extraction
portion (the vehicle height sensor) and the like, thereby improving
the robustness of the accuracy of estimating the relative
displacement value due to an increase/reduction in the sprung mass
even when the number of passengers or the load weight on the
vehicle is changed. The second embodiment will be described,
assigning similar reference numerals to similar components to the
above-described first embodiment and omitting descriptions
thereof.
[0079] A signal processing portion 51 of the state estimation
portion 13 according to the second embodiment includes an FB
control instruction portion 51A, a lateral acceleration calculation
portion 51B, a sprung mass calculation portion 51C, and a
longitudinal acceleration calculation portion 51D, similarly to the
signal processing portion 16 described in the above-described first
embodiment. The FB control instruction portion 51A calculates the
FB (feedback) control instruction based on the signal from the CAN
12. The lateral acceleration calculation portion 51B calculates the
lateral acceleration Ay working on the vehicle based on the signal
from the CAN 12 (for example, the steering angle signal and the
vehicle speed signal of the vehicle).
[0080] However, the sprung mass calculation portion 51C of the
signal processing portion 51 has a function of estimating and
calculating the mass of the vehicle body 1 (the sprung mass M)
based on a signal from the CAN 12 (for example, a signal including
the sensor value of each of the vehicle height sensors 10). The
sprung mass calculation portion 51C in this case can improve the
robustness of the accuracy of estimating the relative displacement
value due to the increase/reduction in the sprung mass M by using a
mass value estimated from a mass estimation logic employing the
vehicle height sensor 10.
[0081] In this manner, according to the thus-configured second
embodiment, the portion 17B for calculating the load change due to
the lateral acceleration Ay can use the mass value estimated from
the mass estimation logic employing the vehicle height sensor 10 in
which the mass M is set as a variable, when calculating the change
in the load .DELTA.W applied to each of the wheels 2 (i.e., the
wheel loads .DELTA.WFL, .DELTA.WFR, .DELTA.WRL, and .DELTA.WRR)
from the above-described equations 3 to 7 based on the sprung mass
M calculated by the sprung mass calculation portion 51C and the
lateral acceleration Ay.
[0082] Further, the portion 17D for calculating the load change due
to the longitudinal acceleration Ax can also use the mass value
estimated from the mass estimation logic employing the vehicle
height sensor 10 in which the mass M is set as a variable, when
calculating the change in the load .DELTA.WAx generated at each of
the wheels 2 from the above-described equations 18 to 19 based on
the sprung mass M calculated by the sprung mass calculation portion
51C and the longitudinal acceleration Ax.
[0083] Further, the vertical relative acceleration calculation
portion 20 (the acceleration calculation portion) can calculate the
relative acceleration .alpha. as indicated by the above-described
equations 3 and 4 with use of the vertical force (the
operation-derived force) calculated by the vertical force
calculation portion 17 and the like and the sprung mass M
calculated by the sprung mass calculation portion 51C (the mass
calculation portion).
[0084] Therefore, the suspension control apparatus can calculate
the division using the mass value estimated from the mass
estimation logic employing the vehicle height sensor 10 when
acquiring the offset amount of the relative displacement based on
the lateral acceleration and the longitudinal acceleration due to
the driver's steering according to the above-described equations 13
and 25, thereby becoming able to improve the robustness of the
accuracy of estimating the relative displacement value due to the
increase/reduction in the sprung mass M.
[0085] Therefore, according to the second embodiment, even when the
number of passengers or the load weight is changed, the suspension
control apparatus can calculate the acceleration using the sprung
mass estimated based on the displacement calculated by the physical
amount calculation portion (for example, the vehicle height sensor
10) and the like, thereby being able to directly take into
consideration the influence due to the change in the sprung mass M.
As a result, the suspension control apparatus can improve the
estimation accuracy when the weight is changed, thereby being able
to improve the ride comfort on the vehicle.
[0086] Next, FIG. 12 illustrates a third embodiment. The present
embodiment is characterized by being configured to also take into
consideration, for example, a gas reaction force (KGas), a friction
(KFriction), a hydraulic pressure (KOil), and a damping force
response (Tdelay), which are forces generated by the damper, in
addition to the above-described jack-up/down force (JF) and
lift-up/down force (GF) as the inertial force derived from the
driver's operation and the force generated due to the suspension
geometry. The third embodiment will be described, assigning similar
reference numerals to similar components to the above-described
first embodiment and omitting descriptions thereof.
[0087] The vertical calculation portion 17 (i.e., the front-wheel
jack-up force estimation portion 17A, the load change calculation
portion 17B, the front-wheel anti-dive/squat force estimation
portion 17C, and the load change calculation portion 17D), the
damper damping force estimation portion 18, and the front-wheel
spring force estimation portion 19 are connected to the input side
of the vertical relative acceleration calculation portion 20.
However, in the third embodiment, a stabilizer spring force
estimation portion 61, a damper gas pressure estimation portion 62,
a damper friction estimation portion 63, a damper oil elastic force
estimation portion 64, and a suspension bush force estimation
portion 65 are further connected to the input side of the vertical
relative acceleration calculation portion 20.
[0088] The stabilizer spring force estimation portion 61 estimates
and calculates the stabilizer reaction force due to the torsional
stiffness of the stabilizer 4F on the front wheel side illustrated
in FIG. 2 based on the roll or the difference in vertical motion
between the front left wheel 2FL and the front right wheel 2FR.
Further, regarding the stabilizer 4R on the rear wheel side
illustrated in FIG. 2, the stabilizer spring force estimation
portion 61 also similarly estimates and calculates the stabilizer
reaction force due to the torsional stiffness based on the roll or
the difference in vertical motion between the rear left wheel 2RL
and the rear right wheel 2RR.
[0089] The damper gas pressure estimation portion 62 is configured
to use air springs (not illustrated) of air suspensions instead of
the coil springs 6 and 9 illustrated in FIGS. 1 and 2 on the
suspension apparatuses 5 and 8 on the front and rear wheel sides,
and estimates and calculates the gas reaction force (KGas) of the
hydraulic fluid (compressed air) supplied to or discharged from
each of the air springs on the front left wheel 2FL, front right
wheel 2FR, rear left wheel 2RL, and rear right wheel 2RR sides as a
damper gas pressure.
[0090] The damper friction estimation portion 63 estimates and
calculates frictional resistance at a sliding portion of each of
the dampers 7 as the friction (KFriction). The damper oil elastic
force estimation portion 64 estimates and calculates the hydraulic
pressure (KOil) of the hydraulic fluid (oil) sealingly contained in
each of the dampers 7 as a damper oil elastic force. The suspension
bush force estimation portion 65 functions to estimate and
calculate a bush and a mount provided on each of the dampers 7 as a
component of the suspension as an equivalent spring constant
(KBushing).
[0091] Further, the damping force response (Tdelay) at each of the
suspension apparatuses 5 and 8 on the front and rear wheel sides
can also be used as an element for improving the estimation
accuracy. Further, the stabilizer reaction force exerted by each of
the stabilizers 4F and 4R on the front and rear wheel sides can
also be added to the following equation 35.
[0092] The following equation 35 indicates an equation of motion of
the suspension apparatus according to the third embodiment. In this
equation, a damping force Fd is calculated based on the damping
fore delay (Tdelay) from the following equation 36, and a damping
force Fc is calculated based on the damping coefficient c from the
following equation 37.
m X 21 = - k Gas X 21 - k Friction X 21 - k oil X 21 - k Bushing X
21 - Fd [ Equation 35 ] Fd = 1 1 + T delay .times. S .times. Fc [
Equation 36 ] Fc = c X . 21 [ Equation 37 ] ##EQU00003##
[0093] In this manner, in the thus-configured third embodiment, the
suspension control apparatus is configured in such a manner that
the stabilizer spring force estimation portion 61, the damper gas
pressure estimation portion 62, the damper friction estimation
portion 63, the damper oil elastic force estimation portion 64, the
suspension bush force estimation portion 65, and the like are
additionally connected to the input side of the vertical relative
acceleration calculation portion 20 besides the front-wheel spring
force estimation portion 19 and the like. Therefore, the suspension
control apparatus can improve the accuracy of calculating
(estimating) the net force Ma before it is divided by the mass M at
the vertical relative acceleration calculation portion 20
illustrated in FIG. 12, by additionally adding each of the items
written on the right side of the above-described equation 35 to,
for example, the left side of the above-described equation 34.
[0094] Next, FIGS. 13 to 15 illustrate a fourth embodiment. The
present embodiment will be described, assigning similar reference
numerals to similar components to the above-described third
embodiment and omitting descriptions thereof. However, the fourth
embodiment is characterized by being configured to include a damper
response delay calculation portion 71 between the damper damping
force estimation portion 18 and the vertical relative acceleration
calculation portion 20.
[0095] Then, the damper response delay calculation portion 71
includes a raise-side (rise-side) primary delay element 72 and a
drop-side (fall-side) primary delay element 73, and a minimum value
selection portion 74 as illustrated in FIG. 14. The minimum value
selection portion 74 selects a smaller damper damping force from a
damper damping force calculated and output via the raise-side
primary delay element 72 (a characteristic line 75 indicated by a
dotted line in FIG. 15) and a damper damping force calculated and
output via the drop-side primary delay element 73 (a characteristic
line 76 indicated by an alternate long and two short dashes line in
FIG. 15).
[0096] Due to this configuration, the damping force determined in
consideration of the damper response delay like a characteristic
line 77 indicated by a solid line in FIG. 15 can be output from the
minimum value selection portion 74 of the damper response delay
calculation portion 71 to the vertical relative acceleration
calculation portion 20. The FB (feedback) control instruction
calculated by the FB control instruction portion 16A based on the
signal from the CAN 12 and the signal of the relative speed output
from the relative speed calculation portion 21 via the delay
operator 24 are input to the damper damping force estimation
portion 18.
[0097] The damping force Fd in the above-described equation 35 has
a response characteristic dependent on the mechanism of each of the
dampers 7, and the response characteristic of each of the dampers 7
includes a characteristic derived from extension (extension stroke)
and compression (compression stroke) relative speeds and a
characteristic derived from the instruction current. Taking them
into consideration as indicated by the above-described equation 36
allows the suspension control apparatus to improve the estimation
accuracy. For example, the damper response delay calculation
portion 71 illustrated in FIG. 14 is formed by combining the
primary delay elements 72 and 73.
[0098] In this manner, in the thus-configured fourth embodiment,
the suspension control apparatus can estimate and calculate the
damping force in consideration of the response delay like the
characteristic line 77 indicated by the solid line in FIG. 15 and
output the damping force Fd as a result of this calculation to the
vertical relative acceleration calculation portion 20. Therefore,
the suspension control apparatus can improve the accuracy of
estimating the relative displacement offset derived from the
driver's operation.
[0099] Next, FIGS. 16 and 17 illustrate a fifth embodiment. The
present embodiment will be described, assigning similar reference
numerals to similar components to the above-described third
embodiment and omitting descriptions thereof. However, the fifth
embodiment is characterized by being configured to include a
control instruction response delay calculation portion 81 between
the FB control instruction portion 16A and the damper damping force
estimation portion 18.
[0100] Then, the control instruction response delay calculation
portion 81 includes a raise-side primary delay element 82 and a
drop-side primary delay element 83, and a minimum value selection
portion 84 as illustrated in FIG. 16. The minimum value selection
portion 84 selects a smaller current value from a current value of
the control instruction output from the FB control instruction
portion 16A via the raise-side primary delay element 82 (a
characteristic line 85 indicated by a dotted line in FIG. 17) and a
current value of the control instruction output from the FB control
instruction portion 16A via the drop-side primary delay element 83
(a characteristic line 86 indicated by an alternate long and two
short dashes line in FIG. 17).
[0101] Due to this configuration, the current value of the control
instruction determined in consideration of the response delay like
a characteristic line 87 indicated by a solid line in FIG. 17 can
be output from the minimum value selection portion 84 of the
control instruction response delay calculation portion 81 to the
damper damping force estimation portion 18. The control instruction
determined in consideration of the response delay that is output
from the control instruction response delay calculation portion 81
(the minimum value selection portion 84) and the signal of the
relative speed output from the relative speed calculation portion
21 via the delay operator 24 are input to the damper damping force
estimation portion 18.
[0102] The instruction current (the current value of the control
instruction) calculated based on the target damping force
calculated by the controller 11 and the current actually flowing in
the circuit affect the raise and drop of the instruction current
due to increases in the temperature of the solenoid and the
temperature of the transistor. The control instruction response
delay calculation portion 81 combines the primary delay elements 82
and 83 as illustrated in FIG. 16, thereby taking the raise and drop
of the current into consideration as the response characteristic of
the instruction current value is illustrated in FIG. 17, thus being
able to correctly estimate the actually generated damping force and
improving the accuracy of estimating the relative displacement
offset derived from the driver's operation.
[0103] In this manner, in the thus-configured fifth embodiment, the
suspension control apparatus can estimate and calculate the current
value of the control instruction in consideration of the response
delay like the characteristic line 87 indicated by the solid line
in FIG. 17 and output the current value as a result of this
calculation to the damper damping force estimation portion 18.
Therefore, the suspension control apparatus can improve the
accuracy of estimating the relative displacement offset derived
from the driver's operation.
[0104] Each of the above-described embodiments has been described
based on the example in which the vehicle height sensor 10 provided
on each of the wheels is used to form the physical amount
extraction portion that detects and estimates the physical amount
based on the relative displacement between the vehicle body 1 and
each of the wheels 2 (i.e., the vertical force and/or the vertical
position). However, the present invention is not limited thereto,
and, for example, a load sensor on each of the wheel sides may be
used to form the physical amount extraction portion. However, for
example, an acceleration sensor that generally acquires the
relative displacement shall not be included in the physical amount
extraction portion.
[0105] Further, in each of the above-described embodiments, the
state estimation portion 13 is assumed to estimate the state of the
vehicle body with use of the vehicle model incorporating the
stabilizer therein. However, the present invention is not limited
thereto, and the state of the vehicle body may be estimated with
use of a vehicle model with the stabilizer removed therefrom.
[0106] Further, each of the above-described embodiments has been
described based on the example in which the damping force
adjustable shock absorber is constructed with use of the damping
force adjustable damper 7 embodied by the semi-active damper.
However, the present invention is not limited thereto, and may be
configured in such a manner that the damping force adjustable shock
absorber is constructed with use of, for example, an active damper
(any of an electric actuator and a hydraulic actuator).
[0107] Possible configurations as the suspension control apparatus
based on the above-described embodiments include the following
examples.
[0108] As a first configuration, a suspension control apparatus
includes damping force adjustable shock absorbers disposed between
a vehicle body and individual wheels of a vehicle, respectively,
and each having a damping characteristic that changes according to
an instruction from an outside, a physical amount extraction
portion configured to detect or estimate a physical amount based on
a relative displacement between the vehicle body and each of the
wheels, and a control device configured to control the damping
characteristic of each of the damping force adjustable shock
absorbers. The control device includes an external force
calculation portion configured to calculate a total external force
working on the vehicle body based on the physical amount output
from the physical amount extraction portion, an operation force
calculation portion configured to calculate an operation-derived
force applied to each of the damping force adjustable shock
absorbers according to a load movement due to an operation on the
vehicle, and a vehicle behavior extraction portion configured to
determine an external force derived from a road surface input by
separating the operation-derived force calculated by the operation
force calculation portion from the total external force calculated
by the external force calculation portion.
[0109] As a second configuration, in the above-described first
configuration, the operation-derived force includes an inertial
force generated due to acceleration/deceleration and steering of
the vehicle or a force generated due to a suspension geometry. As a
third configuration, in the above-described first configuration,
the physical amount extraction portion includes a vehicle height
sensor.
[0110] As a fourth configuration, in the above-described first
configuration, the control device includes a vertical force
calculation portion configured to calculate a vertical force on the
vehicle body, an acceleration calculation portion configured to
calculate an acceleration based on the vertical force calculated by
the vertical force calculation portion, a sprung speed estimation
portion configured to estimate a sprung speed of the vehicle body
based on the acceleration calculated by the acceleration
calculation portion, and a damping characteristic determination
portion configured to determine the damping characteristic of each
of the damping force adjustable shock absorbers based on the sprung
speed estimated by the sprung speed estimation portion. As a fifth
configuration, the above-described fourth configuration further
includes a mass calculation portion configured to calculate a mass
of the vehicle body based on a displacement calculated by the
physical amount extraction portion. The acceleration calculation
portion calculates the acceleration with use of the vertical force
calculated by the vertical force calculation portion and the mass
calculated by the mass calculation portion.
[0111] According to this fifth configuration, the suspension
control apparatus can calculate the acceleration by dividing the
vertical force calculated by the vertical force calculation portion
by the mass calculated by the mass calculation portion. Therefore,
even when the number of passengers or the load weight is changed,
the suspension control apparatus can calculate the acceleration
using the sprung mass estimated based on the displacement
calculated by the physical amount calculation portion (a vehicle
height sensor) and the like, thereby being able to directly take
into consideration the influence due to a change in the sprung
mass. As a result, the suspension control apparatus can improve the
estimation accuracy when the weight is changed, thereby being able
to improve the ride comfort on the vehicle.
[0112] Having described several embodiments of the present
invention, the above-described embodiments of the present invention
are intended to only facilitate the understanding of the present
invention, and are not intended to limit the present invention
thereto. The present invention can be modified or improved without
departing from the spirit of the present invention, and includes
equivalents thereof. Further, the individual components described
in the claims and the specification can be arbitrarily combined or
omitted within a range that allows them to remain capable of
achieving at least a part of the above-described objects or
producing at least a part of the above-described advantageous
effects.
[0113] The present application claims priority under the Paris
Convention to Japanese Patent Application No. 2018-060017 filed on
Mar. 27, 2018. The entire disclosure of Japanese Patent Application
No. 2018-060017 filed on Mar. 27, 2018 including the specification,
the claims, the drawings, and the abstract is incorporated herein
by reference in its entirety.
REFERENCE SIGN LIST
[0114] 1 vehicle body [0115] 2 wheel [0116] 4 stabilizer
(stabilizer mechanism) [0117] 5, 8 suspension apparatus [0118] 7
damping force adjustable damper (damping force adjustable shock
absorber) [0119] 10 vehicle height sensor (physical amount
extraction portion) [0120] 11 controller (control device) [0121] 13
state estimation portion [0122] 14 calculation portion [0123] 15
external force calculation portion (external force calculation
portion) [0124] 16 signal processing portion [0125] 17 vertical
force calculation portion (vertical force calculation portion and
operation force calculation portion) [0126] 18 damper damping force
estimation portion (damping characteristic determination portion
and operation force calculation portion) [0127] 19 front-wheel
spring force estimation portion (operation force calculation
portion) [0128] 20 vertical relative acceleration calculation
portion (acceleration calculation portion) [0129] 21 relative speed
calculation portion (sprung speed estimation portion) [0130] 22
relative displacement calculation portion [0131] 23 vehicle
behavior extraction portion (vehicle behavior extraction portion)
[0132] 51C sprung mass calculation portion (mass calculation
portion)
* * * * *